OX-TRAN Model 2/22 Operator’s Manual
Maintenance
MOCON, Inc.
Revision R
7-5
Maintaining the Oxygen (Coulox) Sensor
Under normal use, the Coulox sensor supplied with your OX-TRAN Model 2/22 should last a year or more.
The sensor could be damaged by accidents or by misuse such as continual exposure to high concentrations
of oxygen. The Coulometric oxygen sensor (Coulox) does not require calibration. If you choose to calibrate
the sensor the procedures are described in Appendix G.
Verifying Oxygen Sensor (Coulox) Performance
You may want to occasionally verify sensor performance by measuring the transmission rate of material
with known characteristics. Certified films are available for this purpose. The “Permeant Sensor Adjustment
Test ” described in Appendix G should be performed using a Certified Film.
Replacing the Coulox Sensor
When the Coulox sensor needs to be replaced please contact MOCON in the USA at (763) 493-6370.
Caution:
Do not attempt to replace the Coulox sensor. This should only be done by an
authorized MOCON Technical Services Representative.
When a sensor is becoming depleted, you will notice a decrease in its response. The best time to observe
this is when the sensor is bypassed after a test; a healthy sensor will react quickly and drop to 5 percent of
the test reading in less than 10 minutes. A damaged or depleted sensor will take much longer to respond.
Usually a depleted sensor exhibits a reduction in efficiency and the measured values tend to read on the
low side. When you observe these symptoms the Coulox sensor should be replaced.
Maximizing Coulox Sensor Life
The useful life of the Coulox sensor is determined by the following factors:
Cathode depletion
A new unused sensor has a nickel cadmium anode. Oxygen entering the sensor
reacts with the cathode material to produce cadmium hydroxide. When most of the
cadmium has been converted to cadmium hydroxide, the sensor response time slows
and efficiency declines.
Cathode depletion is proportional to the Oxygen Input Rate. The most effective way
to increase sensor life is to reduce the oxygen input rate.
Electrolyte depletion Electrolyte depletion is usually caused by water loss. The Coulox sensor uses a
patented system that minimizes moisture loss. It is however, possible to dry-out the
sensor by exposing it to excessive levels of dry carrier gas.
The amount of oxygen input to the sensor can be reduced by the following means:
•
Use a lower O
2
% concentration instead of 100% oxygen to set up the test gradient. Using
21% O
2
for the Test Gas will reduce the oxygen input rate by approximately a factor of five.
•
Use a foil mask to reduce the test area. A 5 cm
2
foil mask will reduce the oxygen input rate to
the sensor by a factor of ten.
•
Using a Conditioning period. When conditioning time is used the sensor is taken off line for a
period of time. This can prolong its useful life of the sensor.